Active video smoke detection (AVSD) is the name that has been coined by Xtralis Pty Ltd for particle detection systems (most preferably smoke detection systems) that use video analysis techniques to detect smoke in an air volume that is actively illuminated, e.g. by a laser or other electromagnetic (EM) radiation source.
Systems and methods for performing AVSD have been described in international patent publications WO 2004/102498 and WO 2006/001723 in the name of VFS Technologies Pty Ltd, the contents of which are incorporated herein by reference for all purposes.
The basic system disclosed in those documents is one in which a laser beam is directed across an air volume being monitored. An image sensor is positioned such that it can capture images of at least part of the beam. The captured images are analysed to determine whether smoke is present in the volume by determining the level of scattered EM radiation captured in the images.
As noted in those patent publications one problem that may be faced by such system is that of objects other than smoke entering the beam or field of view of the image sensor. This can have several effects; firstly it can cause a false alarm by imitating the effect of smoke. Secondly, encroaching objects may prevent the system from detecting smoke by blocking the path of the beam across the volume being monitored or by blocking the view of part of the beam by the image sensor. Thirdly, it may be unsafe if a person (or animal) passes through the beam. Thus, such systems need mechanisms and methods for both preventing the encroachment of objects into the beam, and for the amelioration of the negative effects on the system when such an encroachment occurs.
Another issue to consider is the set-up and maintenance of such a system. An AVSD system will typically have a EM radiation source shining a EM radiation beam across an extended distance. In most circumstances system components will need to be accurately aligned across this extended distance. Alignment of the components will need to be performed at commissioning and periodically during the operation of the system to ensure correct operation.
Due to the relative difficulty in controlling the environment in air volumes suited to the use of an AVSD system, e.g. large areas, high roofed enclosed areas such as atriums etc. an AVSD system must be sufficiently robust to cope with a wide range of environments. For example such environments often have a wide range of possible background light levels, e.g. differences in lighting levels between day and night; and may also have rapidly fluctuating background light levels.
Accordingly there is a need for methods and systems for improving the sensitivity, usability, and robustness of AVSD systems. Other objects and aspects of embodiments of the present invention will become apparent from the following description.
It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained, understood, regarded it as relevant or combined it in anyway at the priority date.